Login into Moodle from external server

Hi

I want to implement a functionality wherein I want to login to moodle from my external application by using some kind of webservice where I can pass username and password for the existing user in moodle and login into moodle from an external application say .net application.

It would be very helpful if I could get some sort of REST or SOAP API code to login into moodle using external application.

Thanks